With the increasing depth of wells and the number of casing strings used therein, one of the main concerns with the well housings and other well structures on which hangers and other equipment are landed and supported is the tremendous loading of the landing shoulders and the increasing desire to decrease the load area of these shoulders to avoid as much blockage of the interior of the housing as possible. Another factor in these housings on which casings are supported is that a flow passage is needed to allow circulation and cementing after the hanger has been landed thereon and before the annulus seal is set.
U.S. Pat. No. 4,528,738 discloses one hanger structure which is intended to support extremely heavy loads by utilizing an upper and a lower landing ring which coact with each other and with grooves in the wall of the housing against which they are set to distribute the load being supported over a greater area and thus reduces the individual stress in the housing support structure.
U.S. Pat. No. 4,595,063 provides the support of a plurality of concentric casing strings directly and totally and independently of all other strings and hangers by a plurality of load ring slips that are components of a packoff assembly.
U.S. Pat. No. 4,615,544 discloses a subsea wellhead system including a breech block connection in which the bearing area of the breech block teeth is greater than the bearing area of the housing seat for the casing hanger.